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envelope

n.
US //ˈɛnvəˌɫoʊp// en·ve·lope
  1. 1 for letters (n.)
    A2 Elementary

    a flat paper container used for mailing letters or cards.

    a flat, usually rectangular paper container with a sealable flap, used for enclosing letters or documents for post.

    Example

    She licked the back of the envelope and pressed it shut.

    Example

    The solicitor handed over a thick manila envelope containing the original deeds to the property.
    Pitfall
    I need to envelope this letter.
    I need to envelop this letter.

    The noun is 'envelope' (with an 'e' at the end), but the verb meaning 'to wrap' is 'envelop' (no 'e' at the end).

  2. 2 technical limits (n.)
    C1 Advanced Technical Engineering

    the limits of what a machine or system can safely do.

    the set of performance limits within which a technological system, especially an aircraft, can operate safely.

    Example

    The test pilot was careful not to fly outside the safety envelope.

    Example

    By incorporating carbon-fibre components, the design team managed to push the performance envelope of the prototype significantly.

    Usage

    Commonly used in the idiom 'push the envelope' to mean testing the limits of what is possible.
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  1. 3 outer covering (n.)
    B2 Upper Intermediate Academic Science

    a layer that wraps around or covers something else.

    a natural or artificial covering that encloses an object or structure.

    Example

    The virus is protected by an outer envelope made of proteins.

    Example

    The building's thermal envelope was upgraded with high-performance insulation to reduce energy loss during the winter months.
  2. 4 sound shape (n.)
    C2 Proficiency Technical Music

    the way a sound changes in volume over time.

    the variation in the amplitude of a sound signal over time, typically defined by attack, decay, sustain, and release.

    Example

    He adjusted the envelope on the synthesizer to make the notes sound softer.

    Example

    The sound engineer manipulated the ADSR envelope to give the lead synth a more percussive, aggressive character.
  3. 5 balloon bag (n.)
    C1 Advanced Technical

    the large fabric bag that holds the gas in a hot-air balloon.

    the fabric structure of an aerostat that contains the lifting gas.

    Example

    The ground crew checked the envelope for small holes before the flight.

    Example

    The hot-air balloon's nylon envelope expanded rapidly as the burners blasted heat into the opening.
Etymology 1

PIE word *h₁én From French enveloppe. The engineering sense is derived from flight envelope. The verb is from the noun.

Etymology 2

See envelop.

Idioms2 entries

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